A closer look at the ‘characteristic’ width of molecular cloud filaments

Properties of the hierarchical structures of interstellar molecular clouds are discussed. Particular attention is paid to the statistical correlations between velocity dispersion and size, and between the magnetic field strength and gas density. We investigate the formation of some hierarchical structures with the help of numerical MHD simulations using the ENLIL code. The simulations show that the interstellar molecular filaments with parallel magnetic field and molecular cores can form via the collapse and fragmentation of cylindrical molecular clouds. The parallel magnetic field halts the radial collapse of the cylindrical cloud maintaining its nearly constant radius ∼0.1 pc. The observed filaments with perpendicular magnetic field can form as a result of the magnetostatic contraction of oblate molecular clouds under the action of Alfvén and MHD turbulence. The theoretical density profiles are fitted with the Plummer-like function and agree with observed profiles of the filaments in Gould's Belt. The characteristics of molecular cloud cores found in our simulations are in agreement with observations.

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“…However, it should be noted that distribution of mean filaments width may be broader than determined in observations (Panopoulou et al 2017).…”

Section: Conclusion and Discussionmentioning

confidence: 56%

Hierarchical structure of the interstellar molecular clouds and star formation

Dudorov

Khaibrakhmanov

2017

Open Astronomy

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“…Other authors like Juvela et al (2012) and Hennemann et al (2012) have however reported larger widths of about 0.3 pc, while Panopoulou et al (2016) reported a lesser width of 0.06 ± 0.04 pc. Ysard et al (2013) reported widths varying by a factor of 4, while Panopoulou et al (2017) concluded that a single characteristic width of filaments is inconsistent with observations, and that the narrow distribution is an averaging effect.…”

Section: Filament Widths In Comparison With Herschel Dust Mapsmentioning

confidence: 95%

Morphology and Kinematics of Filaments in the Serpens and Perseus Molecular Clouds

Dhabal

Mundy

Rizzo

et al. 2018

ApJ

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We present H 13 CO + (J=1-0) and HNC (J=1-0) maps of regions in Serpens South, Serpens Main and NGC 1333 containing filaments. We also observe the Serpens regions using H 13 CN (J=1-0). These dense gas tracer molecular line observations carried out with CARMA have an angular resolution of ∼ 7 , a spectral resolution of ∼ 0.16 km/s and a sensitivity of 50-100 mJy/beam. Although the large scale structure compares well with the Herschel dust continuum maps, we resolve finer structure within the filaments identified by Herschel. The H 13 CO + emission distribution agrees with the existing CARMA N 2 H + (J=1-0) maps; so they trace the same morphology and kinematics of the filaments. The H 13 CO + maps additionally reveal that many regions have multiple structures partially overlapping in the line-of-sight. In two regions, the velocity differences are as high as 1.4 km/s. We identify 8 filamentary structures having typical widths of 0.03 − 0.08 pc in these tracers. At least 50% of the filamentary structures have distinct velocity gradients perpendicular to their major axis with average values in the range 4 − 10 km s −1 pc −1 . These findings are in support of the theoretical models of filament formation by 2-D inflow in the shock layer created by colliding turbulent cells. We also find evidence of velocity gradients along the length of two filamentary structures; the gradients suggest that these filaments are inflowing towards the cloud core.

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“…Characterising filaments is fraught with difficulty, and caution must be observed whilst deriving global properties from their mean profiles (e.g. Panopoulou et al 2017). …”

Section: Appendix A: Channel Mapmentioning

confidence: 99%

Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13

Williams

Peretto

Avison

et al. 2018

A&A

112

110

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Context. Converging networks of interstellar filaments, i.e. hubs, have been recently linked to the formation of stellar clusters and massive stars. Understanding the relationship between the evolution of these systems and the formation of cores/stars inside them is at the heart of current star formation research. Aims. The goal is to study the kinematic and density structure of the SDC13 prototypical hub at high angular resolution to determine what drives its evolution and fragmentation. Methods. We have mapped SDC13, a ∼1000 M infrared dark hub, in NH 3 (1,1) and NH 3 (2,2) emission lines, with both the Jansky Very Large Array and Green Bank Telescope. The high angular resolution achieved in the combined dataset allowed us to probe scales down to 0.07pc. After fitting the ammonia lines, we computed the integrated intensities, centroid velocities and line widths, along with gas temperatures and H 2 column densities. Results. The mass-per-unit-lengths of all four hub filaments are thermally super-critical, consistent with the presence of tens of gravitationally bound cores identified along them. These cores exhibit a regular separation of ∼ 0.37 ± 0.16 pc suggesting gravitational instabilities running along these super-critical filaments are responsible for their fragmentation. The observed local increase of the dense gas velocity dispersion towards starless cores is believed to be a consequence of such fragmentation process. Using energy conservation arguments, we estimate that the gravitational to kinetic energy conversion efficiency in the SDC13 cores is ∼ 35%. We see velocity gradient peaks towards ∼ 63% of the cores as expected during the early stages of filament fragmentation. Another clear observational signature is the presence of the most massive cores at the filaments' junction, where the velocity dispersion is the largest. We interpret this as the result of the hub morphology generating the largest acceleration gradients near the hub centre. Conclusions. We propose a scenario for the evolution of the SDC13 hub in which filaments first form as post-shock structures in a supersonic turbulent flow. As a result of the turbulent energy dissipation in the shock, the dense gas within the filaments is initially mostly sub-sonic. Then gravity takes over and starts shaping the evolution of the hub, both fragmenting filaments and pulling the gas towards the centre of the gravitational well. By doing so, gravitational energy is converted into kinetic energy in both local (cores) and global (hub centre) potential well minima. Furthermore, the generation of larger gravitational acceleration gradients at the filament junctions promotes the formation of more massive cores.

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A closer look at the ‘characteristic’ width of molecular cloud filaments

Cited by 82 publications

References 52 publications

Hierarchical structure of the interstellar molecular clouds and star formation

Hierarchical structure of the interstellar molecular clouds and star formation

Morphology and Kinematics of Filaments in the Serpens and Perseus Molecular Clouds

Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13

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